Effects of boron nitride impurities on the elastic properties of carbon nanotubes

The molecular dynamics method is used in this paper to investigate the effect of boron nitride (BN) impurities on the elastic properties of armchair (5, 5) (10, 10) and zigzag (9, 0) (18, 0) single-walled carbon nanotubes (SWCNTs). The results show the Young's moduli of armchair (5, 5) (10, 10) and zigzag (9, 0) (18, 0) SWCNTs with no impurities to be 948 GPa, 901 GPa and 804 GPa, 860 GPa, respectively. When the armchair SWCNTs are doped with BN, their Young's modulus decreases slightly. However, an increase in the doping ratio beyond a certain point does not cause any further reduction in the modulus, which continues to fluctuate at about 800 GPa and 760 GPa, respectively. The zigzag SWCNTs behave somewhat differently. When they are doped with BN, their Young's moduli drop quickly, and then rise as the doping ratio increases until it reaches 100% (i.e. boron nitride nanotubes are formed), at which point the Young's moduli of the nanotubes are 780 GPa and 835 GPa, respectively, 97% that of the corresponding pure SWCNTs. The effect of a high ratio of BN on zigzag SWCNTs is thus negligible. The reasons for this phenomenon are analyzed according to the law of electron cloud coupling between two atoms, which comes from the local density approximation (LDA) and is based on density functional theory (DFT).